The present invention relates to a frequency converter, in particular, to a frequency converter for the local oscillator of a super-heterodyne transmitter/receiver. According to the present invention, a single oscillator is employed as a local oscillator of a transmitter, a transmitting frequency converter of a transmitter, and a local oscillator of a receiver.
In a prior super-heterodyne transmitter/receiver, separate local oscillators are utilized for the transmitter and receiver. That is to say, the first local oscillator is utilized for the transmitter, and the second local oscillator for the receiver. The local oscillator is very expensive in a wireless device, in particular, a local oscillator for frequencies higher than the UHF band, since many coaxial cables and/or waveguides must be utilized, heavy high frequency components must be utilized, and the manufacturing cost becomes high.
Accordingly, a basic local system having a single local oscillator for both a transmitter and a receiver has been proposed. However, a prior single local oscillator system has the disadvantage that the center frequency of a transmitter oscillator is altered by the modulation signal, and the fluctuation of the transmitter oscillator causes cross-talk in a receiver.